Photocatalyst formulations and coatings

ABSTRACT

An apparatus includes a substrate having a surface, and a transparent semiconductor photocatalyst layer secured to the surface of the substrate, wherein the photocatalyst layer includes titanium oxide and a component selected from a fluorescent dye, ultra-fine glitter, indium tin oxide, aluminum zinc oxide, silver nitrate, and combinations thereof. The photocatalyst coating may be formed on a substrate using a formulation that includes an aqueous mixture of titanium oxide and amorphous titanium peroxide, wherein the aqueous mixture may further include one of the components. A method of forming the photocatalyst coating may include applying an aqueous mixture of titanium oxide and amorphous titanium peroxide to a surface of the substrate, wherein the photocatalyst coating includes a fluorescent dye, ultra-fine glitter, indium tin oxide, aluminum zinc oxide, and/or silver nitrate. The aqueous mixture may then be dried and heated to 100 degrees Celsius or greater.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a nonprovisional patent application claiming thebenefit of U.S. provisional patent application Ser. No. 63/062,579 filedon Aug. 7, 2020, which application is incorporated by reference hereinin its entirety.

BACKGROUND

The present disclosure relates to photocatalyst formulations,photocatalyst coatings, the use of photocatalyst coatings, andsubstrates securing a photocatalyst coating.

BACKGROUND OF THE RELATED ART

A photocatalyst is a material that can absorb light and use that energyto create electron-hole pairs with the photocatalyst. In turn, eachelectron-hole pair can generate free radicals from oxygen or watermolecules that contact the photocatalyst surface bearing theelectron-hole pair. These free radicals, such as hydroxyl radicals andother reactive oxygen species, may circulate in the air or an aqueousfluid until the free radicals react with other materials. However, thephotocatalyst is neither consumed nor degraded during generation of thefree radicals.

A beneficial use of a photocatalyst is for the generation free radicalsto reduce or eliminate contaminants or other undesirable materials inair or aqueous fluids. Hydroxyl radicals, for example, are highlyreactive and can react with a wide variety of materials, such asgreenhouse gases, volatile organic compounds, viruses, bacteria, pollen,mold spores and the like. The free radicals or other reactive oxygenspecies may eliminate or degrade some contaminants, such as methane,ammonia, carbon monoxide or formaldehyde, to form harmless products,such as water and carbon dioxide. Other contaminants, such as virusesand bacteria, may be killed, neutralized, or destroyed by reaction withthe free radicals or other reactive oxygen species without necessarilybeing reduced down to water and carbon dioxide.

BRIEF SUMMARY

Some embodiments provide an apparatus comprising a substrate having asurface, and a transparent or translucent semiconductor photocatalystlayer secured to the surface of the substrate, wherein the transparentsemiconductor photocatalyst layer includes titanium oxide and acomponent selected from a fluorescent dye, ultra-fine glitter, indiumtin oxide, aluminum zinc oxide, and/or silver nitrate.

Some embodiments provide a formulation for forming a photocatalystcoating on a substrate, comprising an aqueous mixture of titanium oxideand amorphous titanium peroxide, wherein the aqueous mixture furtherincludes a fluorescent dye, ultra-fine glitter, indium tin oxide,aluminum zinc oxide, and/or silver nitrate.

Some embodiments provide an apparatus comprising a substrate having asurface, a transparent or translucent binder layer secured to thesurface of the substrate, and a transparent semiconductor photocatalystlayer secured to the transparent binder layer, wherein the transparentbinder layer and/or the transparent semiconductor photocatalyst layerincludes titanium oxide and a component selected from a fluorescent dye,ultra-fine glitter, indium tin oxide, aluminum zinc oxide, and/or silvernitrate.

Some embodiments provide an apparatus comprising a substrate having asurface, and a photocatalyst coating secured on exposed surface of thesubstrate, wherein the photocatalyst coating includes titanium oxide anda component selected from a fluorescent dye, ultra-fine glitter, indiumtin oxide, aluminum zinc oxide, and/or silver nitrate. Non-limitingexamples of the apparatus include a substrate selected from a floortile, countertop, appliance handle, doorknob, light emitting device,light cover, switch, and keyboard. Optionally, the exposed surface ofthe substrate may be a decorative surface, and the photocatalyst coatingmay be transparent.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a photocatalyst absorbing light and producing oneor more reactive species capable of degrading an organic pollutant.

FIG. 2 is a diagram of a substrate and a photocatalytic coating securedto a surface of the substrate.

FIG. 3 is a diagram of a transparent substrate in the form of alightbulb having a photocatalytic coating secured to an exterior surfaceof the lightbulb.

FIG. 4 is a diagram of a substrate, a binder layer secured to thesubstrate, a photocatalytic coating secured to the binder layer, and alight source directing light on the photocatalytic coating.

FIGS. 5A-D are diagrams of a photocatalyst-coated substrate beingcontaminated by touching and then being decontaminated by the mechanismof action of the photocatalyst.

DETAILED DESCRIPTION

The various embodiments provide photocatalytic formulations,photocatalytic coatings that are prepared using the photocatalyticformulations, substrates and devices that are coated with thephotocatalytic coating, methods for preparing the formulation, andmethods for forming the coating on a substrate or device.

In some embodiments, the formulation is a solution (a yellow suspension)including anatase titanium oxide having a pH in a range from about 7.5to about 9.5 and a particle size in a range from about 8 to about 20nanometers (nm). The formulation may be prepared by adding an alkalihydroxide, such as aqueous ammonium hydroxide or sodium hydroxide to anaqueous titanium salt solution, then washing and separating theresulting titanium hydroxide. The resulting light bluish-white titaniumhydroxide may then be treated with an aqueous hydrogen peroxide solutionto obtain a yellow, transparent solution of amorphous titanium peroxidesol having a pH in a range from about 6.0 to about 7.0 and a particlesize in a range from about 8 to about 20 nm. The amorphous titaniumperoxide solution may be heated to a temperature of 100 degrees Celsiusor higher, which has been found to reduce the band gap of the resultingphotocatalytic coating.

When a semiconductor, such as titanium dioxide, in the coating isirradiated with light (photons) whose wavelength has an energy greaterthan a band gap of the semiconductor, an electron is promoted to theconduction band such that the electron may participate in anoxidation-reduction reaction with molecules that are in contact with thesemiconductor surface. Such a semiconductor is referred to as a“photocatalytic semiconductor” or merely a photocatalyst. Photocatalystsmay be in the form of a powder and may be used as suspended in asolution or may be used as supported on a substrate. From the standpointof photocatalytic activity, the photocatalyst may have greater activitysuspended in a solution owing to the greater surface area. However,practical applications of the photocatalyst typically require thephotocatalyst to be supported on a substrate.

It is believed that a photon of light having sufficient energy causesseparation of an electron (negatively charged) and a hole (positivelycharged) in the solid phase photocatalyst(s) of the coating. While anelectron may cause a reductive reaction with molecules that are incontact with the coating adjacent the electron, the hole may cause anoxidative reaction with molecules that are in contact with the coatingadjacent the hole. Accordingly, the photocatalyst may support bothoxidative reactions (i.e., oxidation) and reductive reactions (i.e.,reduction) at various points over the surface of the photocatalystcoating. These reactions may, without limitation, include the oxidationof water molecules (i.e., moisture in the air or liquid water) and/orthe reduction of oxygen molecules (i.e., oxygen in the air or oxygendiffused in liquid water). For example, the oxidation reaction mayproduce a hydroxyl radical (⁻OH) and the reduction reaction may producea super oxygen radical (O₂ ⁻). These hydroxyl radicals and super oxygenradicals are very oxidative and non-selective, such that these radicalswill react with and destroy organic contaminants with only harmless andnaturally occurring byproducts (i.e., water (H₂O) and carbon dioxide(CO₂)). Accordingly, the hydroxyl radicals produced by thephotocatalysts are effective at eliminating volatile organic compounds(VOCs), viruses, bacteria, pollen, mold, and other pollutants andcontaminants.

In some embodiments, the formulation may further include a fluorescentdye that is incorporated into the coating. After applying theformulation to a surface and allowing it to dry and harden, theresulting coating is transparent. This prevents any simple determinationwhether the coating has achieved full coverage over a particularsubstrate or whether the coating remains adhered to the substrate overtime. However, with a fluorescent dye added to the formulation that isused to form the coating, ultraviolet light that is directed at thephotocatalytic coating will cause the fluorescent dye in the coating toemit a fluorescence that can be easily seen. The observation offluorescence makes it easy to determine that the coating covers theintended area of the substrate and/or is still attached to thesubstrate. The amount of fluorescent dye that is added to theformulation may vary from one application to the next. However, thefluorescent dye may be less than 1 percent of the formulation and ispreferably about 0.5 percent of the formulation, such as from 0.4 to 0.6percent of the formulation. A non-limiting example of a fluorescent dyeis triethanolamine (N(CH₂CH₂OH)₃). A suitable concentration is betweenabout 2 and about 10 mg/m² of the coated surface, and most preferablyabout 5 mg/m² of the coated surface.

Similarly, in some embodiments, the formulation may include ultra-fineglitter added to the formulation to assist in ascertaining whether thecoating has achieved full coverage over an intended area of a substrateand/or whether the coating remains adhered to the substrate over time.

In some embodiments, the formulation may further include an additionalphotocatalytic oxide for the purpose of enhancing the photocatalyticaction of the coating. For example, the further photocatalytic oxide maybe selected from indium tin oxide (ITO) and/or aluminum zinc oxide(Al₂O₅Zn₂). Including one or both of these photocatalytic oxides in theformulation may reduce the band gap of the coating formed with theformulation. Reducing the band gap means that the coating will have agreater level of photocatalytic action in response to a given amount oflight exposure. So, if the coating includes titanium dioxide and one ormore of indium tin oxide (ITO) and/or aluminum zinc oxide (Al₂O₅Zn₂),then the band gap of the coating may be reduced below the band gap fortitanium dioxide alone.

The band gap energy of a semiconductor is the minimum energy required toexcite an electron in the valence band and promote that electron intothe conduction band where it can participate in conduction. In graphs ofthe electronic band structure of insulators and semiconductors, the bandgap generally refers to the energy difference between the top of thevalence band and the bottom of the conduction band. The addition ofindium tin oxide may, for example, decrease the indirect band gap oftitanium dioxide present in the coating. It is believed that the indiumtin oxide may increase electron mobility of the semiconductor.Accordingly, less energy is required to move an electron from thevalence band to the conduction band. When the titanium dioxide issubjected to photons, the photons pass their energy to electrons in thetitanium dioxide material. This energy provides those electrons withenough energy to move from the valence band to the conduction band. Theamount of energy required to make this happen is called a band gap orenergy gap.

Anatase titanium dioxide is an indirect band gap semiconductor thatpossesses a band gap value ranging from about 3.2 to about 3.35electronvolts (eV) in the thin film state. As a non-limiting example,the thin film may have a thickness between about 75 and about 300microns. The band gap of a thin film of anatase titanium dioxide can bereduced to about 2 eV with heating. Formulations including a furtherphotocatalytic oxide, such as indium tin oxide (ITO) and/or aluminumzinc oxide (Al₂O₅Zn₂), are believed to reduce the band gap to about 1eV.

In some embodiments, silver nitrate (AgNO₃) may be added to theformulation to provide the resulting coating with antimicrobial activityeven in the absence of light. Coatings that contain silver nitrate maybe beneficially applied to surfaces that a person is likely to contact.For example, countertops, doorknobs, mobile phones, touch screens andcontrol panels are frequently touched by one or more people. A surfacethat supports the coating with silver nitrate may immediately begindecontaminating any organic matter that is left on the surface by aperson's touch even in the dark.

In some embodiments, an ultra-fine glitter may be added to theformulation.

In one embodiment, a photocatalyst coating may be formed on the surfaceof a substrate and may then be either air dried or heat dried. Heatdrying is preferred as it has been found to decrease the band gap. Thephotocatalyst coating may be formed as a single layer coating containingthe photocatalyst or may be formed as a two-layer coating including abinder layer followed by a photocatalyst layer.

Some embodiments provide a method for forming a photocatalytic coatingon a substrate. The photocatalyst coating may be secured directly to asurface of the substrate or secured to an optional binder layer thatsecured to the substrate. For example, an amorphous titanium peroxidesol may be used as a binder to secure the photocatalyst to thesubstrate. A “sol” is a colloid made of very small solid particles in acontinuous liquid medium.

In some embodiments, the substrate may be the lightbulb cover, such as abulb made of glass, fused quartz or plastic. The light within the coveror bulb may be produced by an incandescent element (i.e., wirefilament), a fluorescent element (i.e., cathode electrodes and a gas,such as mercury vapor), or a light-emitting diode.

In some embodiments, a method for forming or securing a photocatalyst toa substrate includes applying multiple layers of an amorphous titaniumperoxide sol to the substrate or an optional binder layer. For example,a first layer of an amorphous titanium peroxide sol may be applied ontothe substrate or binder layer, and then a second layer may be appliedonto the first layer, wherein the second layer is made of a mixture ofthe photocatalyst and an amorphous titanium peroxide sol. Optionally,the amorphous titanium peroxide sol may have no photocatalytic function.

Some embodiments provide a photocatalytic body or apparatus prepared inaccordance with one or more of the methods. For example, thephotocatalytic body may include a substrate and a photocatalytic coatingsecured to a surface of the substrate. Optionally, the photocatalyticbody may include a binder layer between the surface of the substrate anda photocatalyst layer.

Some embodiments provide a photocatalyst formulation used in the methodfor forming the photocatalytic coating on a substrate. The photocatalystformulation may be applied directly onto a substrate or onto a layer ofa binder material. Optionally, the binder may be formed from anamorphous titanium peroxide sol.

In some embodiments, an amorphous titanium peroxide sol may be preparedfrom an aqueous solution of a titanium salt, such as titaniumtetrachloride (TiCl₄), by adding an alkali hydroxide, such as aqueousammonium hydroxide or sodium hydroxide. The reaction product formed bythe addition of alkali hydroxide to the aqueous solution of a titaniumsalt is a light bluish-white, amorphous titanium hydroxide (Ti(OH)₄)that may be referred to as ortho-titanic acid (H₄TiO₄). This titaniumhydroxide may be washed and separated, then treated with an aqueoushydrogen peroxide solution to obtain an amorphous titanium peroxidesolution that may be used to form the binder layer and/or used in thephotocatalyst layer. The amorphous titanium peroxide sol may have a pHin a range from about 6.0 to about 7.0, may have a particle size in arange from about 8 nanometers to about 20 nanometers (nm), and mayappear as a yellow transparent liquid. The amorphous titanium peroxidesol is stable when stored at temperatures between about 45 and about 65degrees Celsius over an extended period of about 6 months. The solconcentration may be adjusted to a range from about 1.40% to about 1.60%amorphous titanium peroxide by volume. For example, the concentration ofthe amorphous titanium peroxide sol may be reduced by dilution with aliquid, such as distilled water.

The amorphous titanium peroxide sol may remain in the amorphous form,since amorphous titanium peroxide is not crystallized into the form ofanatase titanium oxide at normal temperatures, such as temperaturesbetween about 45 and about 65 degrees Celsius. The amorphous titaniumperoxide sol has good adherence to a substrate surface, a goodfilm-forming property and is able to form a uniform thin film on almostany substrate. Once the amorphous titanium peroxide sol film has beendried, the dried film or coating is insoluble in water. Conversely, ifthe amorphous titanium peroxide sol is heated to 100 degrees Celsius (°C.) or greater, the amorphous titanium peroxide sol is converted to ananatase titanium oxide sol. Similarly, an amorphous titanium peroxidesol that has been applied to a substrate, and has been dried and fixedon the substrate, may be converted to anatase titanium oxide when heatedto 250 degrees C. or greater.

Some embodiments may use one or more photocatalysts in the photocatalystlayer. Each of the one or more photocatalysts may be independentlyselected from TiO₂, ZnO, SrTiO₃, CdS, CdO, CaP, InP, In₂O₃, CaAs,BaTiO₃, K₂NbO₃, Fe₂O₃, Ta₂O₅, WO₃, SaO₂, Bi₂O₃, NiO, Cu₂O, SiC, SiO₂,MoS₂, MoS₃, InPb, RuO₂, CeO₂ and the like. A preferred photocatalyst istitanium dioxide (TiO₂). A formulation containing titanium dioxide, alsoreferred to as titanium oxide, may be used in the form of a sol.

In some embodiments, a titanium oxide sol may be prepared by heating anamorphous titanium peroxide sol at a temperature of 100° C. or greater,where the amorphous titanium peroxide sol may be prepared as describedabove. The properties of the titanium oxide sol may vary slightlydepending upon the temperature at which the amorphous titanium peroxidesol is heated and the duration of time over which the heating takesplace. For instance, an anatase titanium oxide sol that is formed byheating an amorphous titanium peroxide sol at 100° C. for 6 hours mayhave a pH ranging from about 7.5 to about 9.5, may have a particle sizeranging from about 8 nanometers to about 20 nanometers, and may appearas a yellow suspension.

The titanium oxide sol is stable when stored at normal temperatures overa long time and may form a precipitate on mixing with an acid or a metalaqueous solution. Moreover, the sol may be impeded in its photocatalyticactivity or an acid resistance when Na ions co-exists. The titaniumoxide sol concentration may be adjusted to within a range from about 1%to about 5% by volume, and preferably about 2.70% to about 2.90% byvolume prior to use.

In some embodiments, the substrate may be made of various inorganicmaterials, such as ceramics and glass. In other embodiments, thesubstrate may be made of various organic materials, such as plastics,rubber, wood, and paper. In still other embodiments, the substate may bemade of various metals, such as aluminum, steel and various alloys. Inparticular, the amorphous titanium peroxide sol may bind well withcertain organic polymer resin materials, such as acrylonitrile resin,vinyl chloride resin, polycarbonate resins, methyl methacrylate resin(acrylic resins), polyester resins, and polyurethane resins. Thesubstrate may also be provided in various sizes and shapes, such as ahoneycomb, fibers, a filter sheet, a bead, a foamed body, a smooth flator curved surface, or combinations thereof. Substrates that transmit UVlight therethrough may have the photocatalytic coating applied to aninner or outer surface of the substrate. Still further, thephotocatalytic coatings may be applied to substrates that have alreadybeen coated with other materials.

In some embodiments, the binder layer is formed with materials that willnot be decomposed by the action of the photocatalyst layer. For example,an inorganic binder may be inert to the free radical species generatedby the photocatalytic reactions occurring at the photocatalyst surface.Non-limiting examples of inorganic binders include water glass,colloidal silica, and cement. A preferred inorganic binder may be formedfrom an amorphous titanium peroxide sol. Non-limiting examples oforganic binders that may be inert include fluoropolymers and siliconepolymers.

In some embodiments, a formulation that is used to make thephotocatalytic layer may be a mixed sol including a uniform suspensionof titanium oxide powder in an amorphous titanium peroxide sol. Forexample, the titanium oxide powder may be uniformly suspended in theamorphous titanium peroxide sol by mechanical mixing followed by theapplication of ultrasonic waves.

Next, the titanium oxide sol and the amorphous titanium oxide sol may bemixed to obtain a mixed sol. The mixing ratio may vary depending uponthe end use of the photocatalyst coating. For example, the mixing ratiomay vary depending on the portion of a product to which thephotocatalytic layer is applied and the conditions under which thephotocatalyst layer will be used. Furthermore, the mixing ratio may bedetermined with consideration given to the necessary adherence of thecoating to a substrate, the film-forming properties of the mixture, thecorrosion resistance of the mixture, and the decorativeness of thephotocatalytic layer made by use of the mixed sol. The mixing ratio maybe based upon the types of articles to which the coating is to beapplied. Three group of substrates may be broadly classified as follows:

(1) Those articles which a person may contact or touch, or is highlylikely to contact or touch, and which need decorativeness from a visualstandpoint, e.g. interior tiles, sanitary wares, various types of unitarticles, table wares, exterior materials in buildings, interiorautomotive trims and the like.

(2) Those articles which a person does not contact or touch, butrequires visual decorativeness, e.g. exterior panels for light fittings,underground passage, tunnel, materials for engineering works, andelectrical equipment.

(3) Those articles which a person does not usually contact, touch, orsee and in which the function of decomposing organic matters based on aphotocatalytic function or the properties inherent to semiconductivemetals are utilized, e.g. built-in members in the inside ofwater-purifier tanks, various types of sewage treatment equipment, waterheaters, bath tubs, air conditioners, the hoods of microwave ovens, andother apparatus.

For an article from group (1), a photocatalytic layer may be preparedwith a mixed sol including about 30 weight percent (wt %) or less of thetitanium oxide sol based on a total amount of the mixed sol (i.e., thecombination of titanium oxide sol and an amorphous titanium peroxidesol). Photocatalyst layers formed with this mixing ratio are suitablefor sterilization or decontamination in daily life and also fordecomposition of residual odors. Moreover, the coating surface is sohard that it is free of any wear such as by sweeping or dusting and alsoof any deposition of foreign matters, along with the unlikelihood ofleaving fingerprints on contact. In fact, the coating has been found tohave a hardness from about 7.0 to about 7.2 on the hardness scale.

An example of an article from group (3) is a water-purifier tank. Highphotocatalytic activity is the most important property for aphotocatalyst in a water-purifier tank, where photocatalytic activity isrequired to lower a biological oxygen demand (BOD) in finalwastewater-treated water. A photocatalytic layer suitable for theseapplications may be prepared with a mixed sol including about 70 wt % orgreater of titanium oxide sol based on the amount of the mixed sol(i.e., the combination of titanium oxide sol and an amorphous titaniumperoxide sol). This photocatalytic layer may be poor in decorativenesssince a person does not typically contact, touch or see thephotocatalytic layer.

For an article from group (2), a photocatalytic layer may be preparedwith a mixed sol including from about 20 wt % to about 80 wt % titaniumoxide sol based on a total amount of the mixed sol (i.e., thecombination of titanium oxide sol and an amorphous titanium peroxidesol). This photocatalytic layer exhibits properties intermediate betweenthe photocatalytic layers described above in reference to groups (1) and(3) with respect to the hardness, the adherence of foreign matters, andthe photocatalytic activity.

In some embodiments, a titanium oxide sol, an amorphous titaniumperoxide sol and/or a mixed sol may be applied over a surface of asubstrate using any known process, including, for example, dipping,spraying, brushing, and coating. The results of coating application arefrequently improved by repeating the coating step multiple times.

After applying a layer by any of the processes mentioned above, the sollayer may be dried and solidified to obtain a coating layer, including abinder layer and/or a photocatalyst layer. The sol layer may also bebaked at a temperature ranging from about 200° C. to about 400° C.

In some embodiments, the photocatalytic activity of titanium oxide maybe reduced by the presence of sodium ions. Accordingly, if the substrateor binder layer is subject to decomposition, such as an organic polymerresin that may undergo decomposition by means of a photocatalyst appliedthereto, the substrate or binder layer may be cleaned with a sodiumion-containing material, such as a sodium hydroxide solution, to reducethe extent to which the photocatalyst may decompose the substrate orbinder layer.

It will be noted that where an amorphous titanium peroxide sol is usedas a first layer, the amorphous titanium peroxide may be converted tothe crystals of anatase titanium oxide on heating to 250° C. or greater,thereby causing a photocatalytic function to develop. Accordingly,temperatures lower than 250° C., for example 80° C. or below, may beused for drying and solidification. In this case, sodium ions may beadded to the titanium peroxide sol for the reasons set out above.

In some embodiments, a wavelength (absorption band) of UV light that isnecessary to induce photocatalytic activity, i.e. an excitationwavelength, may be modified by the altering the composition of theformulation (by addition of inorganic pigments or metals) and/oraltering the thermal treatment of the coating. For example, CrO₃ may beadded to the TiO₂ in small amounts so that the absorption band isshifted toward a longer wavelength.

In some embodiments, the photocatalytic layer may be admixed with one ormore metals, such as Pt, Ag, Rh, RuO, Nb, Cu, Sn, and NiO, to assist inthe photocatalytic activity of the photocatalytic layer. These metalsmay be added to the formulation at various point in the preparation ofthe photocatalytic layer.

In some embodiments, a photocatalyst may be supported and fixed on asubstrate without lowering the photocatalytic function of thephotocatalyst, thereby providing a photocatalytic layer which is usableover a long period of time. The photocatalytic layers and coatings maybe used on interior and exterior surfaces and structures of buildingssuch as interior and exterior tiles, sanitary wares, air conditioners,bathtubs and the like, exterior panels of various types of electricequipment such as lighting fittings, interior automotive members, innerwalls of underground passages and tunnels, water-purifier tanks and thelike.

FIG. 1 is a diagram of a photocatalyst 10 absorbing light 12 andproducing one or more reactive species capable of degrading an organicpollutant. The photocatalyst may take the form of a coating or layersecured to a substrate (not shown) or secured to a binder that is itselfsecured to a substrate.

It is believed that a photon of light 12 having sufficient energy causesseparation of an electron 14 (negatively charged) and a hole 16(positively charged) in the solid phase photocatalyst(s) 10. While anelectron 14 may cause a reductive reaction with molecules that are incontact with the photocatalyst 10 adjacent the electron 14, the hole 16may cause an oxidative reaction with molecules that are in contact withthe photocatalyst 10 adjacent the hole 16. Accordingly, thephotocatalyst 10 may support both oxidative reactions (i.e., oxidation)and reductive reactions (i.e., reduction) at various points over thesurface of the photocatalyst coating.

These oxidative and reductive reactions may, without limitation, includethe oxidation of water molecules 18 (i.e., moisture in the air or liquidwater) and/or the reduction of oxygen molecules 20 (i.e., oxygen in theair or oxygen diffused in liquid water). For example, the oxidation ofwater 18 may produce a hydroxyl radical (⁻OH) 22 and the reduction ofoxygen 20 may produce a super oxygen radical (O₂ ⁻) 24. These hydroxylradicals 22 and super oxygen radicals 24 are very reactive andnon-selective, such that these radicals will react with and destroyorganic contaminants or pollutants 26 with only harmless and naturallyoccurring byproducts (i.e., water (H₂O) 28 and carbon dioxide (CO₂) 29).Accordingly, the reactive species 22, 24 produced by the photocatalyst10 are effective at eliminating volatile organic compounds (VOCs),viruses, bacteria, pollen, mold, and other organic contaminants orpollutants 26.

FIG. 2 is a diagram of a substrate 30 and a photocatalyst coating 10secured to a surface 32 of the substrate 30. The substrate 30 providesphysical support for a thin layer of the photocatalyst 10. Optionally,the photocatalyst could cover all surfaces of a substrate, one side orthe other side of substrate, or a limited region of a substrate. A widevariety of substrate materials may be used. Furthermore, the thicknessand composition of the photocatalyst may also vary as described herein.

In some embodiments, the photocatalyst 10 may include a fluorescent dyeor ultra-fine glitter. The inclusion of fluorescent dye or ultra-fineglitter makes it possible to detect coverage of the photocatalyst overthe substrate during or after manufacturing or detect damage that mayoccur to the photocatalyst coating over time. It is easy for a personmaking a visual inspection of the photocatalyst 10 having ultra-fineglitter to detect a damaged or uncovered area 33 due to the absence of aglittery appearance. Due to the transparent or translucent nature of thephotocatalyst 10, the damaged or uncovered area 33 may otherwise avoidvisual detection. In an alternative embodiment, the photocatalyst 10 mayinclude a fluorescent dye, such as triethanolamine (N(CH₂CH₂OH)₃). Thefluorescent dye shows up when exposed to light of a wavelength known tocause the fluorescence, such as a wavelength from 390 to 420 nanometers.Uncovered or damages areas 33 are visually detectable by the absence offluorescence in those areas.

FIG. 3 is a diagram of a lightbulb 40 including a transparent substrate42 in the form of a bulb or globe having a photocatalyst coating 44secured to an exterior surface of the transparent substrate 42. Whilelight 12 from the sun or other sources may activate the photocatalyst44, the lightbulb 40 includes its own light source, such as a wirefilament 46, that emits light (photons), from within the bulb orglobe-shaped substrate 42. The substrate may be made of variousmaterials, such as glass, fused quartz or plastic. However, for lightfrom the wire filament 46 to reach the photocatalyst and induce chargeseparation (i.e., the production of electrons and holes) the substratemay be transparent or translucent. As a result, the photocatalyticactivity of the photocatalyst coating 44 is not dependent upon externallight sources and can degrade organic pollutants in the air or watersurrounding the lightbulb 40 as long as the lightbulb is switched on(see switch 47) to supply electrical current from a source of electricalcurrent 48, such as an alternating current source or battery. Still, thephotocatalyst 44 is formed on the external surface of the substrate 42where it makes contact with oxygen and water in the air surrounding thelightbulb 40. The reactive species formed as a result of light beingabsorbed by the photocatalyst will then circulate in the air surroundingthe lightbulb until the reactive species contact and degrade an organicpollutant.

It should be recognized that the lightbulb 40 of FIG. 3 isrepresentative of other embodiments of a light-emitting device. Forexample, the wire-filament 46 that is present in most incandescentlightbulbs may be replaced with one or more light-emitting diode (LED)or the components of a fluorescent lightbulb (i.e., fluorescent gas andcathodes). Furthermore, the lightbulb 40 may have a wide variety ofshapes as desired for aesthetic or functional purposes. Still further,the photocatalyst 44 may be formed using any of the formulations andmethods disclosed herein.

FIG. 4 is a diagram of a substrate 50, a binder layer 52 secured to thesubstrate 50, a photocatalytic coating 10 secured to the binder layer52. Light may be directed onto the photocatalyst from the top or, if thesubstrate is transparent or translucent, from the bottom. The binderlayer may be used to improve attachment of the photocatalyst to thesubstrate. However, the binder layer may also include one or morephotocatalysts and may contribute additional photocatalytic activity orcapacity to the overall structure. The binder layer 52 may also have adifferent composition than the photocatalyst layer 10 and/or may beprocessed under different conditions than the photocatalyst layer 10.

FIGS. 5A-D are diagrams of a substrate 60 having a photocatalyst coating62 that is being contaminated by touching and then being decontaminatedby the mechanism of action of the photocatalyst coating 62. Thephotocatalyst coating 62 is supported by the substrate 60 and isdirectly exposed to air, moisture and light in the environment. Whilethe light is illustrated reaching the photocatalyst from the exposed(environment) side, it is also possible for a transparent or translucentsubstrate to allow light to reach the photocatalyst from the substrateside.

In FIG. 5A, a person's finger 63 is contaminated with an organicmaterial 64, such as a virus, bacteria, mold, fungus, oil, dirt or thelike. Light absorbed by the photocatalyst 62 may, as describedpreviously (see FIG. 1), form reactive species from the water and oxygenin the air that comes into contact with the photocatalyst 62.Accordingly, the reactive species may circulate in the air to degradethe organic material 64 even in the absence of actual contact betweenthe organic material 64 and the photocatalyst 62.

In FIG. 5B, the person's finger 63 contacts the photocatalyst 62. FIG.5C illustrates the photocatalytic activity of the photocatalyst 62absorbing light and transforming an oxygen molecule (O₂) into a superoxygen radical (O₂ ⁻). The super oxygen radical (O₂ ⁻) may then degradesome of the organic material 64 to form carbon dioxide and water. Withcontinued exposure to light, the photocatalyst 62 continues to formreactive species, such as the super oxygen radical (O₂ ⁻), to degradeadditional organic material 64. Because the photocatalyst 62 is notconsumed or degraded in the photocatalytic process, the effectiveness ofthe photocatalyst 62 may continue indefinitely. As shown in FIG. 5D,eventually most or all of the organic material 64 can be eliminated. Formany surfaces that are frequently touched by people, such as public doorknobs and bathroom faucets, the ability to passively decontaminate thesurface at all times is a substantial benefit to health and hygiene.

Some embodiments are more particularly described by way of the followingReference Solutions and Examples, which should not be construed aslimiting the scope of the embodiments.

Reference Solution 1 (Preparation of an Amorphous Titanium Peroxide Sol)

A 1:70 dilution by volume of a 50% solution of titanium tetrachloride(TiCl₄) with distilled water and a 1:10 dilution by volume of a 25%solution of ammonium hydroxide (NH₄OH) with distilled water were mixedat a ratio by volume of 7:1 for a neutralization reaction. Aftercompletion of the neutralization reaction, the pH was adjusted to fallinto a range from about 6.5 to about 6.8, and the mixture was allowed tostand for about an hour to form a gel, followed by discarding of thesupernatant liquid. Distilled water was added to the resultant Ti(OH)₄in an amount of about 4 times the amount of gel, followed by sufficientagitation to mix the water and gel thoroughly, and allowing the mixtureto stand. The washing with distilled water was repeated until nochlorine ion was detected in the supernatant liquid. Silver nitrate maybe used to detect chlorine. Finally, the supernatant liquid wasdiscarded to leave only a gel. In some cases, the gel may be subjectedto centrifugal dehydration to obtain a better gel. 210 ml of an aqueous35% hydrogen peroxide (H₂O₂) solution was divided into two halves andone half was added to 3600 ml of light yellowish white Ti(OH)₄ every 30minutes, followed by agitation at about 5 degrees Celsius overnight toobtain about 2500 ml of a yellow transparent amorphous titanium peroxidesol.

If the temperature of the solutions is not suppressed in the abovesteps, there is the possibility that water-insoluble matter, such asmetatitanic acid deposits, may form. Thus, it is preferred to carry outall the steps while suppressing the temperature of the solutions, suchas by directing a fan to blow room temperature or chilled air over thesolution.

Reference Solution 2 (Preparation of Titanium Oxide Sol from AmorphousTitanium Peroxide Sol)

Heating the amorphous titanium peroxide sol at 100° C. will cause theamorphous titanium peroxide sol to be converted to anatase titaniumoxide after a period of about 3 hours and will cause a furtherconversion to an anatase titanium oxide sol on heating for about 6hours. Moreover, when the amorphous titanium peroxide sol is heated at100° C. for 8 hours, it assumes a light yellow, lightly suspendedfluorescence. On concentration of the amorphous titanium peroxide sol, ayellow opaque matter may be obtained. Further, when the amorphoustitanium peroxide sol is heated at 100° C. for 16 hours, a verylight-yellow matter is obtained. This matter, more or less, lowers indry adherence on comparison with that obtained by heating at 100° C. for6 hours. Heating the amorphous titanium peroxide sol (prior to applyingover a substrate) for a longer period of time (i.e., about 6 hours)during preparation of the formulation results in a formulation that willform a coating having greater photocatalytic activity but loweradherence to the substrate relative to a coating that is formed with thesame starting formulation that was heated for a shorter period of time(i.e., about 3 hours) during preparation of the formulation.

The titanium oxide sol was lower in viscosity than the amorphoustitanium oxide and is employed after concentration to 2.5 wt % becauseof the ease in dipping.

EXAMPLE 1

The decomposition of organic substances was tested using photocatalyticcoatings made from different mixing ratios between the amorphoustitanium peroxide sol and the titanium oxide sol. A KERAMIT decorativesheet having dimensions of about 150 mm long, about 220 mm wide, andabout 4 mm thick was used as a substrate. Mixed sols having differentmixing ratios were each coated onto one of the substrates in a thicknessof about 2 micrometers (μm) by spraying and then dried from normalambient temperatures to 70° C., followed by baking at about 400° C. for30 minutes to obtain five types of photocatalytic bodies, whereindifferent types of photocatalysts were each supported on the substrate.

These five photocatalytic bodies were each placed in a test containerand a colored solution of an organic substance was added into each testcontainer to a depth of 1 centimeter (cm), covering the photocatalyticbody or substrate. The colored solution was a 1:30 dilution of POLLUXRed OM-R (SUMIKA COLOR CO., LTD.) which was an aqueous dispersion (redliquid) of Monoazo Red. In order to prevent the evaporation of thecolored solution in the container, the container was covered with afloat glass (capable of cutting a wavelength of 300 nm or below). Two UVradiators (each being a 20 W blue color fluorescent tube) were set at 5cm above the test container and at 9.5 cm from the substrate, whilekeeping the two UV radiators apart from each other at a distance of 13cm. The individual photocatalytic bodies were irradiated with UV lightand the duration of irradiation was measured. The organic matter wasjudged to be completely decomposed when the color of the coloredsolution was bleached.

The photocatalytic body with 100% titanium oxide sol applied onto thesubstrate was as able to bleach the color in 72 hours from commencementof the test. Thus, the capability of decomposing the organic substance,i.e., the photocatalytic function, was good, but a residue after thedecomposition was great in amount.

The photocatalytic body with 100% of the amorphous titanium peroxide solapplied onto the substrate bleached the color in 150 hours fromcommencement of the test. So, the ability of the amorphous titaniumperoxide sol to decompose the organic substance, i.e. the photocatalyticfunction, was poorer than that using 100% of the titanium oxide sol.Nevertheless, the amorphous titanium peroxide sol exhibited betteradherence, film-forming property, corrosion resistance anddecorativeness.

The photocatalytic bodies having a mix of amorphous titanium peroxidesol and titanium oxide sol produced results that were intermediate ofthose for either of the two sols alone. For example, the color of thecolored solution was bleached in 78 hours for a 1:3 mixing ratio of theamorphous titanium peroxide sol and the titanium oxide sol, bleached in102 hours for a 1:1 mixing ratio, and bleached in 120 hours for a 3:1mixing ratio, respectively. Accordingly, the photocatalytic function wasin reverse proportion to the adherence, film-forming property, corrosionresistance and decorativeness. Thus, a diversity of applications (i.e.,substrate material, portions of articles where the photocatalyst is tobe applied, and use conditions) may be accommodated by changing themixing ratio.

EXAMPLE 2

An acrylic resin plate and a methacrylic acid resin plate were eachprovided as a substrate. These resin plates were, respectively, immersedin a 2% sodium hydroxide solution at 80° C. for 30 minutes, then washedwith water and dried. The amorphous titanium peroxide sol prepared inReference Solution 1, to which 0.5% of a surface-active agent was added,was coated onto the acrylic resin plate and the methacrylic acid resinplate by repeating a dipping step about 3 or 4 times to form a firstlayer. Drying was affected at 70° C. for 10 minutes.

A second layer was formed over the first layer by separately coatingfive different mixtures of the amorphous titanium peroxide sol and thetitanium oxide sol at the same mixing ratios used as in Example 1 byrepeating a dipping step about 3 or 4 times. Drying and solidificationwas affected at a temperature of 120° C. for 3 minutes for the acrylicresin plate and was stopped for the methacrylic resin plate when thetemperature of a dryer reached 119° C. The results of the photocatalyticfunction for each plate were similar to those of Example 1. However, thephotocatalyst layers that were formed over a first layer hadsignificantly better adhesion to the resin plates and were less likelyto decompose the resin plates.

EXAMPLE 3

A highly water-absorbing and commercially available tile was used as asubstrate. The tile was washed with a neutral detergent, dried andapplied with a surface-active agent. A photocatalyst formulation wasformed by adding 1 part by weight of titanium oxide powder “ST-01”(ISHIHARA SANGYO KAISHA Ltd) to 50 parts of the amorphous titaniumperoxide sol (pH 6.4) prepared in Reference 1, followed by mechanicalagitation for about 15 minutes and then agitation by means of ultrasonicwaves in order not to leave flocs. Dipping was affected at a rate in therange of about 0.3 to about 0.5 cm/second, followed by drying overnightat 30° C. The coated substrate was then baked at 400° C. for 30 minutesto make a photocatalytic layer.

The photocatalyst layer formed in this manner was firmly bonded to thetile surface over a long time. By contrast, merely coating the tile witha dispersion of the titanium oxide powder in distilled water did notresult in good bonding.

EXAMPLE 4

A float glass which had been degreased and treated with a surface-activeagent was coated on the surface thereof with a suspension of glass beadsby means of a spray gun several times. After drying at 40° C., thecoating was baked at 700° C. for 30 minutes. The float glass on whichthe glass beads were fixed was further coated with a photocatalystcomposition used in Example 3, dried and baked at 400° C. for 30 minutesto obtain a photocatalytic layer. This photocatalytic layer was stronglybonded to the glass beads that were fixed on the float glass over a longtime.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to limit the scope of the claims.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,components and/or groups, but do not preclude the presence or additionof one or more other features, integers, steps, operations, elements,components, and/or groups thereof. The terms “preferably,” “preferred,”“prefer,” “optionally,” “may,” and similar terms are used to indicatethat an item, condition or step being referred to is an optional (notrequired) feature of the embodiment.

The corresponding structures, materials, acts, and equivalents of allmeans or steps plus function elements in the claims below are intendedto include any structure, material, or act for performing the functionin combination with other claimed elements as specifically claimed.Embodiments have been presented for purposes of illustration anddescription, but it is not intended to be exhaustive or limited to theembodiments in the form disclosed. Many modifications and variationswill be apparent to those of ordinary skill in the art after readingthis disclosure. The disclosed embodiments were chosen and described asnon-limiting examples to enable others of ordinary skill in the art tounderstand these embodiments and other embodiments involvingmodifications suited to a particular implementation.

What is claimed is:
 1. An apparatus, comprising: a substrate having asurface; and a transparent semiconductor photocatalyst layer secured tothe surface of the substrate, wherein the transparent semiconductorphotocatalyst layer includes titanium oxide and a component selectedfrom a fluorescent dye, ultra-fine glitter, indium tin oxide, aluminumzinc oxide, and/or silver nitrate.
 2. The apparatus of claim 1, whereinthe component is a fluorescent dye.
 3. The apparatus of claim 1, whereinthe component is ultra-fine glitter.
 4. The apparatus of claim 1,wherein the component is indium tin oxide.
 5. The apparatus of claim 1,wherein the component is aluminum zinc oxide.
 6. The apparatus of claim1, wherein the component is silver nitrate.
 7. The apparatus of claim 1,wherein the substrate is a transparent material selected from glass,fused quartz and plastic.
 8. The apparatus of claim 7, furthercomprising: a light-emitting element disposed adjacent to the substrateto direct light through the transparent substrate material to thetransparent semiconductor photocatalyst layer.
 9. The apparatus of claim8, wherein the light-emitting element is selected from a light-emittingdiode and an incandescent filament.
 10. The apparatus of claim 1,further comprising: a binder layer secured between the surface of thesubstrate and the transparent semiconductor photocatalyst layer.
 11. Theapparatus of claim 10, wherein the binder layer is transparent and thesubstrate is transparent.
 12. The apparatus of claim 11, furthercomprising: a light-emitting element disposed adjacent to the substrateto direct light through the transparent substrate and through thetransparent binder layer to the transparent semiconductor photocatalystlayer, wherein the light-emitting element is selected from alight-emitting diode and an incandescent filament.
 13. The apparatus ofclaim 10, wherein the binder layer includes titanium oxide.
 14. Theapparatus of claim 10, wherein the binder layer includes an inorganicbinder selected from water glass, colloidal silica, and cement.
 15. Theapparatus of claim 10, wherein the binder layer includes an organicbinder selected from fluoropolymers and silicone polymers.
 16. Theapparatus of claim 1, wherein the transparent semiconductorphotocatalyst layer further includes a photocatalyst selected from ZnO,SrTiO₃, CdS, CdO, CaP, InP, In₂O₃, CaAs, BaTiO₃, K₂NbO₃, Fe₂O₃, Ta₂O₅,WO₃, SaO₂, Bi₂O₃, NiO, Cu₂O, SiC, SiO₂, MoS₂, MoS₃, InPb, RuO₂, and/orCeO₂.
 17. The apparatus of claim 1, wherein the titanium oxide is in theform of TiO₂.
 18. A formulation for forming a photocatalyst coating on asubstrate, comprising: an aqueous mixture of titanium oxide andamorphous titanium peroxide, wherein the aqueous mixture furtherincludes a fluorescent dye, ultra-fine glitter, indium tin oxide,aluminum zinc oxide, and/or silver nitrate.
 19. The formulation of claim15, wherein the aqueous mixture has a pH in a range from about 7.5 toabout 9.5 and the titanium oxide has a particle size in a range fromabout 8 to about 20 nanometers.
 20. A method of forming a photocatalystcoating on a substrate, comprising: applying an aqueous mixture oftitanium oxide and amorphous titanium peroxide to a surface of thesubstrate wherein the photocatalyst coating includes a fluorescent dye,ultra-fine glitter, indium tin oxide, aluminum zinc oxide, and/or silvernitrate; drying the aqueous mixture; and heating the aqueous mixture to100 degrees Celsius or greater.